Self-stabilizing dynamic diaphragm for broad bandwidth acoustic energy source

ABSTRACT

An apparatus for estimating a property in a borehole penetrating the earth, the apparatus having: a carrier configured to be disposed in the borehole; and an acoustic transducer disposed at the carrier and configured to at least one of transmit and receive an acoustic wave used to estimate the property, the acoustic transducer comprising an acoustic diaphragm; wherein the acoustic diaphragm includes a surface in communication with a plurality of structural members configured to increase the rigidity of the surface, the surface being configured to interface with a medium that propagates the acoustic wave.

CROSS-REFERENCE TO RELATED APPLICATIONS AND PRIORITY CLAIM

This application claims the benefit of U.S. Provisional Application Ser.No. 61/187,430, entitled “SELF-STABILIZING DYNAMIC DIAPHRAGM FOR BROADBANDWIDTH ACOUSTIC ENERGY SOURCE”, filed Jun. 16, 2009, under 35 U.S.C.§119(e), which is incorporated herein by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention disclosed herein relates to acoustic measurements and, inparticular, to performing the measurements in a borehole.

2. Description of the Related Art

Exploration and production of hydrocarbons generally requires accurateand precise measurements of earth formations, which may containreservoirs of the hydrocarbons. The reservoirs are accessed by drillingboreholes into the earth formations. Well logging is one technique usedto perform the measurements from within the boreholes.

In one type of well logging referred to as wireline logging, a loggingtool supported by an armored cable is conveyed through a borehole. Thearmored cable generally contains electrical cables for supplying powerto the logging tool and communicating with the tool. The logging toolincludes those components such as sensors and processors used to performthe measurements. As the logging tool is conveyed through the borehole,the measurements are performed at various depths. The measurements areassociated with the depths at which they were performed and displayed asa log.

Various types of measurements can be made to produce a log. One type ofmeasurement involves measuring the velocity of sound in an earthformation. Many characteristics of the earth formation such as type of amaterial, amount of a material, and porosity of a material can beestimated by knowing the velocity of sound in the earth formation as afunction of depth.

For example, a sound wave may be emitted that penetrates the earthformation and is reflected back. If it is known that the earth formationis composed of a certain type of material and that the pore spaces ofthe material are filled with water, then it is possible to determine theporosity based on a measurement of the speed of the sound wave.

An acoustic logging tool is used to measure the velocity of sounddownhole. In general, the acoustic logging tool includes at least oneacoustic transmitter to emit a sound wave, at least one acousticreceiver to receive the sound wave, and a processor to process data fromthe tool to estimate the velocity of the sound wave. The transmitter andreceiver may each be referred to as an acoustic transducer. Aconventional acoustic transducer for use downhole operates over a rangeof about ten to fourteen kilohertz. Unfortunately, a wider rangeespecially on the low side is more desirable for the many types ofacoustic measurements that can be performed downhole.

Therefore, what are needed are techniques for transmitting and receivinga sound wave having a wide frequency range downhole. Preferably, thesound wave can cover the frequency range of one to fifteen kilohertz.

BRIEF SUMMARY OF THE INVENTION

Disclosed is a an apparatus for estimating a property in a boreholepenetrating the earth, the apparatus having: a carrier configured to bedisposed in the borehole; and an acoustic transducer disposed at thecarrier and configured to at least one of transmit and receive anacoustic wave used to estimate the property, the acoustic transducercomprising an acoustic diaphragm; wherein the acoustic diaphragmincludes a surface in communication with a plurality of structuralmembers configured to increase the rigidity of the surface, the surfacebeing configured to interface with a medium that propagates the acousticwave.

Also disclosed is a method for estimating a property in a boreholepenetrating the earth, the method including: conveying a carrier throughthe borehole, the carrier having at least one acoustic transducerconfigured to at least one of transmit and receive an acoustic wave usedto estimate the property, the at least one acoustic transducercomprising an acoustic diaphragm wherein the acoustic diaphragmcomprises a surface in communication with a plurality of structuralmembers configured to increase the rigidity of the surface, the surfacebeing configured to interface with a medium that propagates the acousticwave; transmitting an acoustic wave into the borehole using the at leastone acoustic transducer; and receiving the acoustic wave using the atleast one acoustic transducer to estimate the property.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter, which is regarded as the invention, is particularlypointed out and distinctly claimed in the claims at the conclusion ofthe specification. The foregoing and other features and advantages ofthe invention are apparent from the following detailed description takenin conjunction with the accompanying drawings, wherein like elements arenumbered alike, in which:

FIG. 1 illustrates an exemplary embodiment of an acoustic logging tooldisposed in a borehole penetrating the earth;

FIGS. 2A and 2B, collectively referred to as FIG. 2, depict aspects ofan acoustic transducer;

FIGS. 3A, 3B, 3C, and 3D, collectively referred to as FIG. 3, depictaspects of an acoustic diaphragm used in the acoustic transducer;

FIG. 4 A, 4B, and 4C, collectively referred to as FIG. 4, depict moreaspects of the acoustic diaphragm;

FIG. 5 illustrates a cross-sectional view of an exemplary embodiment ofthe acoustic transducer;

FIG. 6 illustrates a three-dimensional view of the acoustic sensor;

FIGS. 7A and 7B, collectively referred to as FIG. 7 depict aspects offrequency response of the acoustic diaphragm;

FIG. 8 depicts other aspects of the frequency response of the acousticdiaphragm;

FIG. 9 depicts aspects of a pressure transfer function of the acoustictransducer in comparison to the pressure transfer function of two priorart acoustic transducers; and

FIG. 10 presents one example of a method for estimating a downholeproperty.

DETAILED DESCRIPTION OF THE INVENTION

Disclosed are exemplary embodiments of techniques for transmitting andreceiving an acoustic wave having a wide frequency range. In particular,the transmitting and the receiving are performed in a boreholepenetrating the earth. The wide frequency range, in general, extends atleast from one to fifteen kilohertz for a frequency range of interest inthe borehole. The techniques, which include apparatus and method, callfor using an acoustic transducer for at least one of transmitting andreceiving the acoustic wave with a light weight and rigid acousticdiaphragm. The acoustic diaphragm is a self-stabilizing dynamicstructure having a broad frequency response. The frequency response ofthe acoustic diaphragm is generated by a relatively flat acoustictransfer function over the frequency range of interest with highacoustic energy output at low frequency and high frequency modes.

The light weight and rigid qualities of the acoustic diaphragm areachieved by using an acoustic surface that is stiffened by a pluralityof structural members. In one embodiment, the structural membersintersect to form geometric shapes (or cells) such as triangles. Thegeometric shapes maximize the rigidity of the surface while minimizingthe dynamic mass of the acoustic diaphragm to customize the resonantfrequency and modal deformation of the diaphragm surface for a specificbandwidth of frequency operation. In one embodiment, the acousticdiaphragm including the surface and the plurality of structural membersis machined from one solid piece of material such as aluminum.

Reference may now be had to FIG. 1. FIG. 1 illustrates an exemplaryembodiment of an acoustic logging tool 10 disposed in a borehole 2penetrating the earth 3. The earth 3 can include a geologic formation 14having layers such as 14A-14C. The logging tool 10 is supported in theborehole 2 by an armored cable 8. The armored cable 8 generally includeselectrical power and signal cables for powering and communicating withthe logging tool 10. The logging tool 10 includes an acoustictransmitter 4 (at least one) for transmitting an acoustic wave 5 and anacoustic receiver 6 (at least one) for receiving the acoustic wave 5. Ingeneral, the acoustic wave 5 is reflected back to the logging tool 10 bymaterial in the formation 14.

Still referring to FIG. 1, the logging tool 10 includes an electronicunit 7 for operating the logging tool 10. Operation of the logging tool10 can include operating the acoustic transmitter 4 and the acousticreceiver 6. In addition, the electronic unit 7 can receive and processor record data associated with measuring the speed of the acoustic wave5. Alternatively, the electronic unit 7 can transmit the data forprocessing or recording to a processing system 9 at the surface of theearth 3.

Still referring to FIG. 1, a casing 11 may be disposed in the borehole2. In this embodiment, the acoustic logging tool 10 may be used tomonitor the casing 11 for corrosion, cracks and discontinuities. Thelogging tool 10 can monitor the casing 11 by using the acoustic wave 5to measure a wall thickness of the casing 11.

While the acoustic logging tool 10 is conveyed by the armored cable 8 inthe embodiment of FIG. 1, the logging tool 10 can also be conveyed byslickline or coiled tubing. In addition, the logging tool 10 can beconveyed by a drill string in embodiments known aslogging-while-drilling (LWD) or measuring-while-drilling (MWD). InLWD/MWD applications, the acoustic logging tool 10 may be disposed in adrill collar. When used in the LWD/MWD applications, drilling may betemporarily halted to prevent vibrations while the logging tool 10 isperforming a measurement.

Reference may now be had to FIG. 2. FIG. 2A illustrates an exemplaryembodiment of the acoustic transmitter 4. The acoustic transmitter 4includes an acoustic diaphragm 20 configured to transmit the acousticwave 5. The acoustic diaphragm 20 in FIG. 2A is coupled to a converter21 that is configured to convert energy from the electronic unit 7 intothe acoustic wave 5. FIG. 2B illustrates an exemplary embodiment of theacoustic receiver 6. The acoustic receiver 6 includes the acousticdiaphragm 20 configured to receive the acoustic wave 5. The acousticdiaphragm 20 in FIG. 2B is coupled to the converter 21 configured toconvert the energy of the received acoustic wave 5 into signal energytransmitted to the electronic unit 7. While shown as separate units inFIGS. 1 and 2, the transmitter 4 and the receiver 6 can be combined intoone unit, referred to herein as an acoustic transducer 4,6. Fordiscussion purposes, the acoustic transducer 4,6 can refer to atransmitter, a receiver, or both.

Reference may now be had to FIG. 3. FIG. 3 depicts aspects of theacoustic diaphragm 20 by presenting several views of the diaphragm 20.FIG. 3A illustrates a horizontal side view of the acoustic diaphragm 20.Referring to FIG. 3A, the acoustic diaphragm 20 includes an acousticsurface 30 that is configured to interact with a medium, such as the afluid disposed in the borehole 2, that transmits the acoustic wave 5. Inone embodiment, the acoustic surface 30 is solid (i.e., having noopenings). The acoustic diaphragm 20 also includes a plurality ofstructural members 31 configured to stiffen or increase the rigidity ofthe acoustic surface 30. In addition, the acoustic diaphragm 20 includesa mounting collar 32 configured to mount the diaphragm 20 to theconverter 21.

FIG. 3B illustrates a bottom view of the acoustic diaphragm 20. In theembodiment depicted in FIG. 3B, each structural member 31 intersectswith another structural member 31 to form geometric shapes such as thetriangles shown in FIG. 3B. FIG. 3C illustrates a vertical side view ofthe acoustic diaphragm 20. FIG. 3D illustrates a three-dimensional viewof the acoustic diaphragm 20.

FIG. 4 depicts dimensions (in millimeters) and other aspects of oneembodiment of the acoustic diaphragm 20. Referring to FIG. 4A, theacoustic diaphragm 20 includes a plurality of lobes 40. The plurality oflobes 40 is distinguished from structural members 31 between the lobes40. The structural members between the lobes 40 form a first angle 41with respect to the mounting collar 32 as shown in FIG. 4C. Each lobe 40forms a second angle 42 with respect to the mounting collar 32 as shownin FIG. 2B. The plurality of lobes 40 optimizes the combination ofstiffness to mass distribution to increase the bandwidth of the acousticfrequency response of the acoustic diaphragm 20.

Reference may now be had to FIG. 5. FIG. 5 illustrates a cross-sectionalview of an exemplary embodiment of the acoustic transducer 4,6. Theacoustic transducer 4,6 in FIG. 5 includes a body 57 to which componentssuch as the acoustic diaphragm 20 are attached. The body 57 includes acavity 50, which contains an elastomeric fluid 51 such as silicone. Thecavity 50 with the fluid 51 is used to improve the low frequencyresponse of the transducer 4,6. In one embodiment, the fluid 51 issilicone having a low stiffness (Shore-A Hardness 5). This fluid 51 hasthe effect of lowering the acoustic roll-off frequency well below twokilohertz and, thereby, increasing acoustic output at the two kilohertzoperating mode.

Still referring to FIG. 5, the converter 21 includes a coil 54 adjacentto a magnet 55 supported by support 56. The coil 54 and the magnet 55 inthe embodiment of FIG. 5 are both circular shaped. For transmitting, anelectrical signal sent to the coil 54 causes the coil 54 and theacoustic diaphragm 20 to move with respect to the magnet 55. Forreceiving, movement of the coil 54 with respect to the magnet 55 due tomovement of the acoustic diaphragm 20 generates an electrical signal inthe coil 54

The acoustic transducer 4,6 in the embodiment of FIG. 5 includes a seal52 such as an O-ring to seal the acoustic diaphragm 20 to the body 57.The seal 52 seals the cavity 50 to prevent exposure of the fluid 51 toreactive mud chemicals while still allowing the diaphragm 20 to moverelative to the body 57. The diaphragm 50 in one embodiment includes agroove 53, such as a V-shaped groove, to hold the seal 52.

Reference may now be had to FIG. 6. FIG. 6 illustrates a cross-sectionalthree-dimensional view of the acoustic transducer 4,6.

A frequency response analysis of the acoustic diaphragm 20 was conductedusing numerical simulation. The analysis simulated the diaphragm 20shown in FIGS. 3-6 with the fluid 51 having the Shore A-5characteristic. The results of the analysis are presented in FIGS. 7 and8. FIG. 7A illustrates the acceleration of the diaphragm 20 versusfrequency for an edge point and a center point. FIG. 7B illustrates thephase angle response of the diaphragm 20 versus frequency for the edgepoint and the center point. FIG. 8 illustrates the acceleration of thediaphragm 20 for the center point and the integral of the accelerationacross the acoustic surface 30 versus frequency. The integral of theacceleration over the acoustic surface is a proportional parameter usedto assess acoustic output pressure as function of frequency.

The acoustic transducer 4,6 having the diaphragm 20 shown in FIGS. 3-6was tested in a water tank. Two prior art acoustic transducers were alsotested for comparison purposes. FIG. 9 illustrates a pressure transferfunction (in psi/ampere) versus frequency for the three acoustictransducers. The experimental data in FIG. 9 indicates that the acoustictransducer 4,6 when used as a transmitter generates approximately 4.2times as much acoustic output pressure at the low frequency 2 kilohertzoperating mode as the two prior art acoustic transducers. Theexperimental data also indicates that the acoustic transducer 4,6 whenused as a transmitter generates approximately 3.4 times as much acousticoutput pressure at the high frequency 12 kilohertz operating mode as thetwo prior art acoustic transducers.

FIG. 10 presents one example of a method 100 for estimating a propertyin the borehole 2 penetrating the earth 3. The method 100 calls for(step 101) conveying the acoustic logging tool 10 through the borehole2. Further, the method 100 calls for (step 102) transmitting theacoustic wave 5 into the borehole 2 using the acoustic transducer 4,6.Further, the method 100 calls for (step 103) receiving the acoustic wave5 using the acoustic transducer 4,6 to estimate the property.

The term “carrier” as used herein means any device, device component,combination of devices, media and/or member that may be used to convey,house, support or otherwise facilitate the use of another device, devicecomponent, combination of devices, media and/or member. The logging tool10 is one non-limiting example of a carrier. Other exemplarynon-limiting carriers include drill strings of the coiled tube type, ofthe jointed pipe type and any combination or portion thereof. Othercarrier examples include casing pipes, wirelines, wireline sondes,slickline sondes, drop shots, bottom-hole-assemblies, drill stringinserts, modules, internal housings and substrate portions thereof. Theterm “medium” relates to a material that propagates the acoustic wave 5.Non-limiting examples of the medium include any of or a combination of afluid disposed in the borehole 2, the formation 14, and the casing 11.

In support of the teachings herein, various analysis components may beused, including a digital and/or an analog system. For example, theelectronic unit 7 or the processing system 9 may included the digitaland/or analog system. The system may have components such as aprocessor, storage media, memory, input, output, communications link(wired, wireless, pulsed mud, optical or other), user interfaces,software programs, signal processors (digital or analog) and other suchcomponents (such as resistors, capacitors, inductors and others) toprovide for operation and analyses of the apparatus and methodsdisclosed herein in any of several manners well-appreciated in the art.It is considered that these teachings may be, but need not be,implemented in conjunction with a set of computer executableinstructions stored on a computer readable medium, including memory(ROMs, RAMs), optical (CD-ROMs), or magnetic (disks, hard drives), orany other type that when executed causes a computer to implement themethod of the present invention. These instructions may provide forequipment operation, control, data collection and analysis and otherfunctions deemed relevant by a system designer, owner, user or othersuch personnel, in addition to the functions described in thisdisclosure.

Further, various other components may be included and called upon forproviding for aspects of the teachings herein. For example, a powersupply (e.g., at least one of a generator, a remote supply and abattery), cooling component, heating component, magnet, electromagnet,sensor, electrode, transmitter, receiver, transceiver, antenna,controller, optical unit, electrical unit, electromechanical unit, ormounting bracket may be included in support of the various aspectsdiscussed herein or in support of other functions beyond thisdisclosure.

Elements of the embodiments have been introduced with either thearticles “a” or “an.” The articles are intended to mean that there areone or more of the elements. The terms “including” and “having” andtheir derivatives are intended to be inclusive such that there may beadditional elements other than the elements listed. The conjunction “or”when used with a list of at least two terms is intended to mean any termor combination of terms. The terms “first” and “second” are used todistinguish elements and are not used to denote a particular order.

It will be recognized that the various components or technologies mayprovide certain necessary or beneficial functionality or features.Accordingly, these functions and features as may be needed in support ofthe appended claims and variations thereof, are recognized as beinginherently included as a part of the teachings herein and a part of theinvention disclosed.

While the invention has been described with reference to exemplaryembodiments, it will be understood that various changes may be made andequivalents may be substituted for elements thereof without departingfrom the scope of the invention. In addition, many modifications will beappreciated to adapt a particular instrument, situation or material tothe teachings of the invention without departing from the essentialscope thereof. Therefore, it is intended that the invention not belimited to the particular embodiment disclosed as the best modecontemplated for carrying out this invention, but that the inventionwill include all embodiments falling within the scope of the appendedclaims.

1. An apparatus for estimating a property in a borehole penetrating theearth, the apparatus comprising: a carrier configured to be disposed inthe borehole; and an acoustic transducer disposed at the carrier andconfigured to at least one of transmit and receive an acoustic wave usedto estimate the property, the acoustic transducer comprising an acousticdiaphragm; wherein the acoustic diaphragm comprises a surface incommunication with a plurality of structural members configured toincrease the rigidity of the surface, the surface being configured tointerface with a medium that propagates the acoustic wave.
 2. Theapparatus of claim 1, wherein the surface comprises a circular shape. 3.The apparatus of claim 2, wherein the acoustic diaphragm comprises amounting ring disposed concentrically to the surface and configured tomount the acoustic diaphragm to a converter configured to least one ofconvert energy into movement of the diaphragm and convert movement ofthe diaphragm into energy.
 4. The apparatus of claim 3, wherein theconverter comprises a coil in electromagnetic communication with amagnet, the coil being configured to at least one of receive energy tomove the diaphragm and transmit energy from the movement of thediaphragm.
 5. The apparatus of claim 4, wherein the coil and magnet aredisposed concentrically to the surface of the acoustic diaphragm.
 6. Theapparatus of claim 3, wherein the at least one member is disposedbetween the mounting ring and a perimeter of the surface.
 7. Theapparatus of claim 6, wherein the at least one member forms a firstangle between the mounting ring and the perimeter of the surface.
 8. Theapparatus of claim 7, wherein the acoustic diaphragm comprises aplurality of lobes spaced about the perimeter of the diaphragm, eachlobe forming a second angle between the mounting ring and the perimeterof the surface, the second angle being configured to increase a rigidityto mass distribution ratio.
 9. The apparatus of claim 8, wherein thefirst angle is 111.5 degrees and the second angle is 106.75 degrees. 10.The apparatus of claim 1, wherein the structural members intersect witheach other to form a geometric shape.
 11. The apparatus of claim 10,wherein the geometric shape comprises a triangle.
 12. The apparatus ofclaim 11, wherein an intersection of two of the structural members iscurved interior to at least one triangle.
 13. The apparatus of claim 1,wherein the acoustic transmitter comprises an elastomer materialdisposed in a cavity and in communication with the acoustic diaphragm.14. The apparatus of claim 13, wherein the elastomer material issilicone.
 15. The apparatus of claim 1, wherein the acoustic diaphragmis machined from one piece of material.
 16. The apparatus of claim 15,wherein the material is aluminum.
 17. The apparatus of claim 1, whereinthe property is of a formation penetrated by the borehole and is atleast one selection from a group consisting of type of material, amountof material, porosity, and a boundary between layers.
 18. The apparatusof claim 1, wherein the property is of a material disposed in theborehole.
 19. A method for estimating a property in a boreholepenetrating the earth, the method comprising: conveying a carrierthrough the borehole, the carrier comprising at least one acoustictransducer configured to at least one of transmit and receive anacoustic wave used to estimate the property, the at least one acoustictransducer comprising an acoustic diaphragm wherein the acousticdiaphragm comprises a surface in communication with a plurality ofstructural members configured to increase the rigidity of the surface,the surface being configured to interface with a medium that propagatesthe acoustic wave; transmitting an acoustic wave into the borehole usingthe at least one acoustic transducer; and receiving the acoustic waveusing the at least one acoustic transducer to estimate the property. 20.The method of claim 19, wherein the acoustic wave comprises a frequencyfrom a range consisting of one to fifteen kilohertz.
 21. The method ofclaim 19, wherein the method is implemented using a computer programproduct stored on machine-readable media.